Hi David
I am pretty sure if it was USB 3.0 Pioneer would advertise it a bit more. I have no proof, but I am 99% sure it is USB 2.0.
And I think thats also fast enough for the purpose. USB 2.0 Specifications are a max transfer rate of 35 MB/s. With my experiences with the XDJ-R1 (have one myself), I think it reads with around 5-10 MB/s. Takes me under 2 seconds to load a 12 MB file.